The invention relates to a method of controlling a hydrostatic drive, with the recuperation of stored energy.
Hydrostatic drives are often used for driving utility vehicles. In that connection, it is possible, via the hydrostatic drive, to store part of the kinetic energy during the braking operation, and to subsequently recover it. The use of a hydrostatic drive in a closed circuit with a hydraulic pump which is intended to effect delivery in only one direction is proposed in AT 395 960 B. The working line on the delivery side, which connects the hydraulic pump to the hydraulic engine, is connected to a high-pressure reservoir. A second reservoir is present, which is constructed as a low-pressure reservoir and is connected to the working line which is on the suction side with respect to the hydraulic pump. The high-pressure reservoir and also the low-pressure reservoir are permanently connected to the working line on the delivery side and to the working line on the suction side, respectively. During normal traction-type operation, the hydraulic pump effects delivery into the working line on the delivery side. The hydraulic engine is adjustable and is swung out in a first direction for travel purposes. If the vehicle moves into overrunning-type operation, the absorption volume of the hydraulic engine is first of all adjusted in the direction of zero. In order to achieve a braking action, the hydraulic engine is then swung out in the opposite direction. As a result of this, said hydraulic engine effects delivery into the working line which is on the delivery side with respect to the hydraulic pump.
A non-return valve is provided in the working line in order to prevent pressure medium from flowing into said hydraulic pump counter to the latter's direction of delivery. The pressure medium delivered by the hydraulic engine is accordingly delivered to the high-pressure reservoir. The kinetic energy of the vehicle is thereby converted into pressure energy, with an increase in the pressure within the high-pressure reservoir. Balancing of the volume flow takes place by the removal of pressure medium from the low-pressure reservoir.
If the stored energy is to be recovered, pressure medium is removed from the high-pressure reservoir. The hydraulic engine is now swung out in its first direction again, as in the previous traction-type operation. When the pressure medium is relieved of pressure via the hydraulic engine, the latter generates an output moment. The pressure medium which is being conveyed through the hydraulic engine is delivered to the low-pressure reservoir for volume-balancing purposes.
A disadvantage of the known drive is that, for the purpose of removing the pressure medium, the hydraulic engine is loaded with the pressure medium directly from the high-pressure reservoir. In the proposed drive with recuperation of the kinetic energy, it is also necessary to tilt the hydraulic engine beyond its neutral location. In the process, the direction of flow within the hydraulic circuit is partially reversed. Because the pressure medium is fed directly to the hydraulic engine, addition of the moments by utilising the pressure in the high-pressure reservoir and also the torque of an engine driving the hydraulic pump is not possible.